Mayhem is a lunatic, plain and simple.
He was discharged from the military almost as quickly as he enlisted; unfortunately, the private mercenary company he joined afterward weren't too thorough in their background checks. As a result of the atrocities committed from his paws during a routine escort mission, not only did the PMC to fire him, they actively tried to kill him just to stop retaliation from the government. He survived.
He was transferred among numerous asylums for the next few years, with scientists continually baffled by his mental state. Some thought he could be cured with severe neuro-chemical alterations, while others believed he was a lost cause and only deserved to be put out of his "misery." While they were busy deliberating for months, Mayhem himself decided to give them a more obvious answer and escape... by murdering all personnel who got in his way in the process. As a final act of flipping off the people who thought he could be tamed, he castrated himself before leaving for good. There was no question as to his sanity, but by that time it was too late.
He later reappeared as an individual mercenary, taking suicidal jobs by clients who were either desperate, or heartless (due to the massive amounts of collateral damage he was likely to cause, including civilian casualties; he's fascinated with big explosions). No one's sure just how he's able to survive everything he's been through; it's possible he's developing an Aura, while others call him extremely lucky. Jerelle believes there might be a correlation there.
It should come as no surprise that Malivia hired him to aid in destroying the R-Force.

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I tried a slightly different perspective for this one, though I think I might've forgotten about it halfway through the pic XD Still, the smile turned out mostly how I'd hoped (also tried to show some new expressions). Apologies for the poor gun design (though to be fair, it's not as curved as it looks; keep in mind half the rifle butt is hidden behind his arm and it's a trapezoidal shape, not a rectangle).
Considering the mythos behind hyenas, I found it odd that he actually turned out to be a eunuch (my characters practically write themselves without my intervention most of the time; it's almost like watching them come to life for the first time), but I guess that makes stand out even more.
Also, he's another in my group of rogues who I'm contemplating a name change. Any ideas are welcome!

Mayhem copyright Aelius (me)